1. Field of the Invention
The present invention relates to a machining apparatus for carrying out grooving by reciprocating a slide member mounted with a tool at high speed and particularly to a machining apparatus having a mechanism for retaining an axial position of a guide member for guiding the slide member.
2. Description of the Related Art
In a metal mold for molding a diffraction grating or a light guide plate used in a liquid crystal display, hundreds to tens of thousands of grooves need be formed. To form such a large number of grooves in a shorter machining time, a machining apparatus having a high-speed feed shaft is necessary. A linear shaft used in a normal machine tool has large sliding weight and is not suitable for high-speed driving.
As a feed mechanism for achieving high-speed and high-precision machining, there is a known structure combining an air bearing and a linear motor. As a feed shaft of this structure, there is a technique of a machining apparatus for forming fine grooves by reciprocating a slide member (shuttle) mounted with a tool at high speed as disclosed in Japanese Patent Application Laid-open No. 2007-130712 (corresponding to U.S. Patent Publication No. 2007/0103262). A slide member high-speed reciprocating device used in this machining apparatus has a mechanism for reversing the slide member by utilizing repulsive forces between magnets disposed at the slide member and magnets disposed at a guide member for guiding the slide member at stroke ends of the slide member to thereby cancel out reaction in the reversal of the slide member.
The high-speed reciprocating device in the machining apparatus described in the aforementioned patent document carries out only one-way pull cutting. For example, if the pull cutting is carried out only on a forward path of the reciprocation, the slide member mounted with the tool receives machining reaction force only on the forward path. Therefore, an acceleration in a decelerating direction is produced for the slide member to slow down the slide member. On the other hand, because cutting is not carried out on a return path, the slide member does not receive the machining reaction force and is not slowed down by the acceleration in the decelerating direction.
Consequently, the reaction force transmitted to the guide member when the slide member is reversed by the force of the magnets at the stroke end of the reciprocating device is greater in reversal from the return path (at high speed as described above) to the forward path than in reversal from the forward path (at low speed as described above) to the return path.
As a result, the reaction force at one end of the stroke of reciprocation of the slide member is different from that at the other end of the stroke and therefore the guide is moved in a direction in which the machining reaction force is transmitted to the tool. In other words, the machining reaction force is transmitted to the guide through the slide member mounted with the tool. Therefore, a mechanism for supporting the guide member in an axial direction is necessary.
Since the machining apparatus disclosed in the aforementioned patent document does not have a mechanism for resisting the machining reaction force applied to the tool, it is difficult to carry out machining such as heavy cutting and cutting of high-hardness material with heavy cutting loads.
Moreover, the aforementioned reciprocating device employs a hydrostatic oil bearing or a hydrostatic air bearing as a fluid bearing. The hydrostatic oil bearing is not suitable for high-speed driving because of high viscous resistance. Although the hydrostatic air bearing is suitable for high-speed driving but not suitable for machining with a heavy cutting load because of low bearing rigidity.